[WFO-KZ]

It looks like someone swapped out the OEM tap for a vacuum operated tap.
Have you looked inside to see if it has a spring and a diaphragm?

 

[WFO-KZ]

These are usually easily rebuilldable, but you have you get it right, or you end up with an engine full of gas inn the crankcase. Worth opening up though. Use the right size screwdrivers so you don't buggger up the threads, in case they're tight, they usually aren't.

This is where JIS screwdrivers come in handy.

 

[WFO-KZ]

FYI, this bike did not come with a vacuum petcock. Look at the Partzilla diagrams and google the part number.
Someone has added it. Nothing wrong with that, its an upgrade, but unless he knows where it came from it may be hard to order the correct rebuild kit.

 

[WFO-KZ]

Partzilla is showing a vacuum petcock for the 1978 KZ1000-A2 but not for the 1000-B2 Ltd.

And no vacuum petcock for the KZ1000- A1 which is also listed under Partzilla 1978 KZ1000.

I think this is case where Partzilla lists several model years for certain parts all of which are shown under the 1978 designation.

I was looking at the A1 thinking it was 1978 when it is really a 1977 bike.

So I stand corrected, the 1978 A2 did come with a vacuum petcock. Sorry for the confusion.

 

[WFO-KZ]

I have no idea what "spacer" he is referring to. Perhaps kopcicle could enlighten us?

 

[WFO-KZ]

I dunno, but when I zoom in it looks like it is there.

 

[WFO-KZ]

This image from CMS shows what should be the OP's diaphragm assembly. Looks like it does not use a plate and a plate is not shown on Partzilla. Go figure. Maybe I got the wrong part number. This is 16126-1011.